1. Field of the Invention
The present invention relates to a circuit topology, and particularly to a circuit topology for multiple loads on a mother board.
2. Description of Related Art
Signal integrity is an important factor to be taken into account when a printed circuit board (PCB) is designed. A well-designed PCB has an elevated on-off switching speed of integrated circuits, and a high density, compact layout of components. Parameters of the components and of the PCB substrate, a layout of the components on the PCB, and a layout of high-speed signal transmission lines all have an impact on signal integrity. In turn, proper signal integrity helps the PCB and an associated computer system to achieve stable performance. Layout of the components is considered as an important part of signal integrity, sometimes signals that reflect back and forth along transmission line cause what is called “ringing.”
Referring to FIG. 3, a conventional circuit topology coupling a signal transmitting terminal to three signal receiving terminals is shown. A signal transmitting terminal 100 is coupled to three signal receiving terminals 60, 70, 80 via corresponding transmission lines. The distance a signal travels from the signal transmitting terminal 100 to the signal receiving terminal 80 is greater than a distance the signal travels from the signal transmitting terminal 100 to the signal receiving terminals 60, 70. A resistor Rs is set on the transmission line close to the signal transmitting terminal 100 to eliminate signal reflections. Referring to FIG. 4, a graph illustrating signal waveforms 66, 77, 88 respectively obtained at receiving terminals 60, 70, 80 using the circuit topology of FIG. 3 is shown. Signals arriving at the receiving terminal 80 reflect back and forth along the transmission line causing “ringing” at receiving terminals 60, 70.
What is needed, therefore, is a circuit topology which can eliminate the signal reflections and maintain signal integrity.